Vaccines for preventing influenza in healthy children

Differences in Influenza-Specific CD4 T-Cell Mediated Immunity Following Acute Infection Versus Inactivated Vaccination in Children

BACKGROUND

Early childhood influenza infections imprint influenza-specific immune memory, with most studies evaluating antibody specificity. In this study, we examined how infection versus inactivated influenza vaccination (IIV) establish pediatric CD4 T-cell mediated immunity to influenza and whether this poises the immune system to respond differently to IIV the following year.

METHODS

We tracked influenza-specific CD4 T-cell responses in 16 H3N2 infected and 28 IIV immunized children following both initial exposure and after cohorts were revaccinated with IIV the following fall. PBMCs were stimulated with peptide pools encompassing the translated regions of the H3 HA and NP proteins and were then stained to assess CD4 T-cell specificity and function.

RESULTS

Compared to IIV, infection primed a greater magnitude CD4 T-cell response specific for the infecting HA and NP proteins, with more robust NP-specific immunity persisting through year 2. Post infection, CD4 T cells preferentially produced combinations of cytokines that included interferon-γ. Interestingly, age-specific patterns in CD4 T-cell reactivity demonstrated the impact of multiple influenza exposures over time.

CONCLUSIONS

These data indicate that infection and vaccination differentially prime influenza-specific CD4 T-cell responses in early childhood, with these differences contributing to the lasting immunologic imprinting established following early influenza infection.

CLINICAL TRIALS REGISTRATION

NCT02559505.

"The flu… is a little more complicated than a cold": Knowledge, beliefs, and practices related to influenza and influenza vaccination among at-risk populations and health professionals in Peru

BACKGROUND

Influenza is a major source of morbidity and mortality with an annual global attack rate estimated at 5-10% in adults and 20-30% in children. Influenza vaccination is the main strategy for reducing influenza-related morbidity and mortality. Like several other countries, Peru has low vaccination coverage, estimated at 25-50% among young children and older adults. Therefore, the study objective was to explore the knowledge, beliefs, attitudes, and practices related to influenza vaccination among populations at higher risk for infection and/or complications and health professionals in Peru, and their perspectives on health communication channels.

METHODS

This qualitative study was carried out in three cities. We held nine focus groups with pregnant and postpartum women, parents of young children, and older adults. We carried out 25 in-depth interviews with health professionals (HPs) working in, leading or advising immunization-related programs.

RESULTS

HPs correctly identified the causes of influenza and HPs and at risk community members identified major symptoms. Community members had poor awareness of the potential severity of influenza and were generally unaware of influenza-related mortality. Both HPs and community members greatly underestimated the prevalence of influenza in Peru. HPs in our study overestimated major side effects of the influenza vaccine and community members perceived that the vaccine caused illness. HPs missed important opportunities to promote vaccination in patients with minor illness (runny nose, allergies, colds) and community members did not understand that the vaccine should be received annually.

CONCLUSIONS

There is no single strategy that will increase influenza vaccination rates to World Health Organization recommended levels. Instead, it requires multi-faceted commitment from HPs, other healthcare authorities and the government. Addressing important knowledge barriers, specifically negative views regarding the influenza vaccine and the severe morbidity and mortality associated with influenza illness, both in the community and especially among HPs, could have significant impacts.

Hematoma as a cause of a febrile and inflammatory response after tibial fractures

After incurring bilateral tibial fractures and developing sizable hematomas at the trauma sites, a child experienced 4 days of fever with an elevated C-reactive protein level and sedimentation rate. As thrombotic and infectious etiologies were ruled out, the patient's febrile and inflammatory response was likely attributable to hematoma formation. Hematomas are a recognized cause of noninfectious fever. Local release of pyrogenic cytokines within the hematoma may be the source for elevation in temperature and inflammatory markers.

Vaccinating in the Emergency Department, a Novel Approach to Improve Influenza Vaccination Rates via a Quality Improvement Initiative

Supplemental Digital Content is available in the text.

Introduction:

Annual influenza vaccination is recommended for all US children 6 months and older to prevent morbidity and mortality. Despite these recommendations, only ~50% of US children are vaccinated annually. Influenza vaccine administration in the pediatric emergency department (ED) is an innovative solution to improve vaccination rates. However, during the 2017–2018 influenza season, only 75 influenza vaccinations were given in this tertiary care ED. We aimed to increase the number of influenza vaccines administered to ED patients from 75 to 1,000 between August 2018 and March 2019.s

Methods:

Process mapping identified potential barriers and solutions. Key interventions included mandatory vaccine screening, creation of a vaccine administration protocol, education for family, provider, and nursing, a revised pharmacy workflow, and weekly staff feedback. Interventions were tested using plan-do-study-act cycles. The process measure was the percent of patients screened for vaccine status. The primary outcome was the number of influenza vaccines administered. The balancing measures were ED length of stay (LOS), wasted vaccines, and financial impact on the institution.

Results:

We included 33,311 children in this study. Screening for vaccine status improved from 0% to 90%. Of those screened, 58% were eligible for vaccination, and 8.5% of eligible patients were vaccinated in the ED. In total, 1,323 vaccines were administered with no significant change in ED LOS (139 min) and no lost revenue to the hospital.

Conclusions:

We implemented an efficient, cost-effective, influenza vaccination program in the pediatric ED and successfully increased vaccinations in a population that might not otherwise receive the vaccine.

Immunogenicity and safety of a multi-dose quadrivalent inactivated influenza vaccine in individuals aged 6 months to 17 years: a randomized phase III trial

Annual vaccination is the most effective way to prevent seasonal influenza. Influenza vaccines in multi-dose vial (MDV) formats can facilitate timely vaccination of large populations by reducing per-dose costs and cold storage requirements compared to single-dose pre-filled syringe (PFS) formats. MDV vaccines require thiomersal or another preservative to prevent microbial contamination. We conducted a randomized, open-label trial in 302 healthy subjects aged 6 months to 17 years to evaluate the immunogenicity and safety of a quadrivalent influenza vaccine (QIV) in a thiomersal-containing MDV format compared to the licensed thiomersal-free PFS format. Subjects were randomly assigned in a 1:1 ratio to receive the MDV (n = 153) or PFS (n = 149) format. Post-vaccination hemagglutination inhibition titers for all four vaccine strains were ≥4.9-fold higher than baseline titers with no difference in magnitude between the MDV and PFS groups. Seroconversion rates per strain were also comparable between the two groups. There were no differences in reactogenicity or safety between the two vaccine formats. These results showed that the MDV format of QIV was as safe and immunogenic as the PFS format in infants, children, and adolescents. These findings support the use of MDV QIV as a resource-saving alternative for seasonal influenza vaccination.

The burden of laboratory-confirmed influenza infection in Lebanon between 2008 and 2016: a single tertiary care center experience

BACKGROUND

Influenza is a major cause of morbidity and mortality worldwide. Following the 2009 pandemic, there was widened interest in studying influenza burden in all regions. However, since data from the World Health Organization (WHO) Middle East and North Africa (MENA) region remain limited, we aimed to contribute to the understanding of influenza burden in Lebanon.

METHODS

A retrospective chart review extending over a period of 8 seasons from Jan 1st, 2008 till June 30th, 2016 at a tertiary care center in Beirut was performed. All cases confirmed to have influenza based on rapid antigen detection or/and polymerase chain reaction on a respiratory sample were included for analysis. Data on epidemiology, clinical presentation, complications, antiviral use and mortality were collected for analysis.

RESULTS

A total of 1829 cases of laboratory-confirmed influenza were identified. Average annual positivity rate was 14% (positive tests over total requested). Both influenza A and B co-circulated in each season with predominance of influenza A. Influenza virus started circulating in December and peaked in January and February. The age group of 19-50 years accounted for the largest proportion of cases (22.5%) followed by the age group of 5-19 years (18%). Pneumonia was the most common complication reported in 33% of cases. Mortality reached 3.8%. The two extremes of age (< 2 years and ≥ 65 years) were associated with a more severe course of disease, hospitalization, intensive care unit (ICU) admission, complications, and mortality rate. Of all the identified cases, 26% were hospitalized. Moderate-to-severe disease was more likely in influenza B cases but no difference in mortality was reported between the two types. Antivirals were prescribed in 68.8% and antibiotics in 41% of cases. There seemed to be an increasing trend in the number of diagnosed and hospitalized cases over the years of the study.

CONCLUSION

Patients with laboratory-confirmed influenza at our center had a high rate of hospitalization and mortality. A population based prospective surveillance study is needed to better estimate the burden of Influenza in Lebanon that would help formulate a policy on influenza control.

Influenza vaccine effectiveness in children: a retrospective study on eight post-pandemic seasons with trivalent inactivated vaccine

Background and aim of the work:

The global burden of disease attributable to seasonal influenza virus in children is difficult to quantify. Children with chronic medical conditions and healthy children may experience severe or fatal complications. Aim of the study was to estimate the influenza vaccine effectiveness (VE) in a cohort of outpatient children.

Methods:

From 2010 to 2018, a Pediatrician of Parma from the InfluNet network of Emilia-Romagna Region, performed nasal/throat swabs on every child with Influenza-like illness at least 14 days from the vaccination with trivalent vaccine. VE estimates against influenza season, virus type and subtype and age group were evaluated using a test-negative design.

Results:

2,480 swabs were performed. The 57.6% of the analyzed swabs were positive for influenza viruses. Type A (57%) and type B viruses (43%) co-circulated. The 37.1% of type A viruses belonged to subtype A(H3N2), 19.4% to subtype A(H1N1)pdm09. The subtype A(H3N2) was prevalent among children up to 23 months (42.4%) while the type B in the 2-4 (40.7%) and 5-16 year old age groups (49.4%). Overall, 19.9% of the children were vaccinated. The highest prevalence of vaccinated subjects was found in children aged 5-16 (30.5%). The VE against subtype A(H1N1)pdm09 was 63% (95%CI 42.6-76.0), against type B 27.5% (95%CI 7.9-42.9) and against subtype A(H3N2) -14.3% (95%CI - 46.0-10.7).

Conclusions:

Our findings represent a useful contribution to the ongoing debate about the appropriateness of including influenza vaccination for healthy children, 6 months and older, in the updating National Vaccine Prevention Plan (PNPV).

Respiratory Virus Co-infection in Acute Respiratory Infections in Children

Purpose of Review

This investigation aims to understand the role and burden of viral co-infections for acute respiratory illnesses in children. Co-infection can be either viral-viral or viral-bacterial and with new technology there is more information on the role they play on the health of children.

Recent Findings

With the proliferation of multiplex PCR for rapid diagnosis of multiple viruses as well as innovations on identification of bacterial infections, research has been attempting to discover how these co-infections affect each other and the host. Studies are aiming to discern if the epidemiology of viruses seen at a population level is related to the interaction between different viruses on a host level. Studies are also attempting to discover the burden of morbidity and mortality of these viral-viral co-infections on the pediatric population. It is also becoming important to understand the interplay of certain viruses with specific bacteria and understanding the impact of viral-bacterial co-infections.

Summary

RSV continues to contribute to a large burden of disease for pediatric patients with acute respiratory illnesses. However, recent literature suggests that viral-viral co-infections do not add to this burden and might, in some cases, be protective of severe disease. Viral-bacterial co-infections, on the other hand, are most likely adding to the burden of morbidity in pediatric patients because of the synergistic way they can infect the nasopharyngeal space. Future research needs to focus on confirming these conclusions as it could affect hospital cohorting, role of molecular testing, and therapeutic interventions.

Oil-in-water emulsion adjuvants for pediatric influenza vaccines: a systematic review and meta-analysis

Standard inactivated influenza vaccines are poorly immunogenic in immunologically naive healthy young children, who are particularly vulnerable to complications from influenza. For them, there is an unmet need for better influenza vaccines. Oil-in-water emulsion-adjuvanted influenza vaccines are promising candidates, but clinical trials yielded inconsistent results. Here, we meta-analyze randomized controlled trials with efficacy data (3 trials, n = 15,310) and immunogenicity data (17 trials, n = 9062). Compared with non-adjuvanted counterparts, adjuvanted influenza vaccines provide a significantly better protection (weighted estimate for risk ratio of RT-PCR-confirmed influenza: 0.26) and are significantly more immunogenic (weighted estimates for seroprotection rate ratio: 4.6 to 7.9) in healthy immunologically naive young children. Nevertheless, in immunologically non-naive children, adjuvanted and non-adjuvanted vaccines provide similar protection and are similarly immunogenic. These results indicate that oil-in-water emulsion adjuvant improves the efficacy of inactivated influenza vaccines in healthy young children at the first-time seasonal influenza vaccination.

Outbreak detection of influenza-like illness in Prey Veng Province, Cambodia: a community-based surveillance

On June 4, 2016, the Prey Veng Provincial Health Department reported a total of 107 patients with influenza-like illness (ILI) from Chakhlanh village to the Cambodian Ministry of Health. To confirm the outbreak and evaluate its clinical and epidemiological characteristics, the investigation team visited the village and reviewed the case-based surveillance (CBS) data on severe respiratory infection (SRI) and patients' records in health facilities. The team interviewed all households in the village from May 1 to June 5, 2016 and obtained the following data: age, medical history, date of onset, treatment, symptoms, and history of contact with patients or dead poultry. Nasal swab samples were collected from suspected ILI cases to test for influenza virus by RT-PCR. The investigation detected 498 suspected ILI cases, including 288 females. Although the incidence of suspected ILI cases who visited health centers was 63.0 per 1,000 persons per month, the attack rate was 27.1 per 100 population. The major age group was 5-14 years followed by 0-4 years. Major symptoms were cough, fever, runny nose, and headache. Six of seven nasal swab samples were positive for influenza A/H1N1 pdm09 virus. Most children with flu symptoms had contact with previous cases. This study showed that the ILI outbreak might be caused by seasonal influenza A/H1N1 pdm09 spread from person to person. Poor living conditions and poor hygiene and sanitation practices were environmental factors that caused the outbreak. As the CBS system was unable to identify this epidemic, it needs to be improved.

Impact of funding influenza vaccination on coverage among Australian children: a national study using MedicineInsight, a large general practice database

Influenza contributes to morbidity and mortality worldwide. Children are at a higher risk of influenza-related complications and vaccination promotes direct protection and limits transmission. This study aimed to explore influenza vaccination coverage among children in Australian general practice from 2015 to 2018, and patterns in coverage before and after the implementation of state-funded immunization programs. Data from 196,520 'active' patients (3+ consultations in two consecutive years) aged <5 years from 542 Australian general practices were included (MedicineInsight database). Logistic regression models were used to identify associations between vaccination with patient and practice characteristics. The overall vaccination coverage increased more than five times from 2015 (3.9%) to 2018 (19.6%) and varied among states. Children attending practices located in the wealthiest areas were more likely to receive the vaccine and appeared to benefit most from the funding, as the increase in coverage from 2017 to 2018 was greater among them than those attending practices in the least advantaged areas (17 vs. 11 percentage points, respectively). This relationship was not evident when analyzing the patient's socioeconomic level. In conclusion, free influenza vaccinations increase coverage in at-risk populations. Promotional campaigns may be required to maintain higher coverage and target practices located in low-income areas.

Influenza Vaccination Coverage among Registered Nurses in China during 2017-2018: An Internet Panel Survey

Influenza vaccination is recommended for nurses in China but is not mandatory or offered free of charge. The main objective of this study was to determine influenza vaccination coverage and the principal factors influencing influenza vaccination among nurses in China. During 22 March-1 April 2018, we conducted an opt-in internet panel survey among registered nurses in China. Respondents were recruited from an internet-based training platform for nurses. Among 22,888 nurses invited to participate, 4706 responded, and 4153 were valid respondents. Overall, 257 (6%) nurses reported receiving the seasonal influenza vaccine during the 2017/2018 season. Vaccination coverage was highest among nurses working in Beijing (10%, p < 0.001) and nurses working in primary care (12%, p = 0.023). The top three reasons for not being vaccinated were lack of time (28%), not knowing where and when to get vaccinated (14%), and lack of confidence in the vaccine's effectiveness (12%). Overall, 41% of nurses reported experiencing at least one episode of influenza-like illness (ILI) during the 2017/2018 season; 87% of nurses kept working while sick, and 25% of nurses reported ever recommending influenza vaccination to patients. Compared with nurses who did not receive influenza vaccination in the 2017/2018 season, nurses who received influenza vaccination were more likely to recommend influenza vaccination to patients (67% vs. 22%, p < 0.001). Influenza vaccination coverage among nurses was low, and only a small proportion recommended influenza vaccine to patients. Our findings highlight the need for a multipronged strategy to increase influenza vaccination among nurses in China.

Effectiveness of seasonal inactivated influenza vaccination in Japanese schoolchildren: an epidemiologic study at the community level

Influenza vaccination is the most effective method for preventing influenza virus infection. The incidence of influenza is higher in schoolchildren than other age groups. This study evaluated the effectiveness of seasonal inactivated influenza vaccination (IIV) in a community population of schoolchildren during two seasons. This study was a cross-sectional survey of public schoolchildren based on data collected in the 2012/2013 and 2014/2015 seasons. The questionnaire was distributed to all public schoolchildren of target grade in a survey area, and 7945 respondents were included in the analysis. The vaccination status and influenza onset were defined based on the self-reported questionnaire by parents or guardians. Generalized linear mixed models were used to adjust clustering within schools and individual covariates and calculate odds ratios (ORs) and 95% confidence intervals (CIs) for associations between vaccination status and influenza onset. The influenza incidence was higher in the 2015 than the 2013 survey (25% versus 17%), although the vaccination rates were comparable between the two seasons. Receiving one- or two-dose vaccination was more protective against influenza than non-vaccination in both the 2013 (OR, 0.77; 95%CI, 0.65-0.92) and 2015 (OR, 0.88; 95%CI, 0.75-1.02) surveys. Full vaccination was also more protective in both the 2013 (OR, 0.75; 95%CI, 0.62-0.89) and 2015 (OR, 0.86; 95%CI, 0.74-1.00) surveys. Seasonal IIV was protective against influenza for Japanese schoolchildren in a community-based real-world setting. The difference in clinical effectiveness of IIV between the two seasons was likely due to the antigenic mismatch between the circulating and vaccine strains.

The 100 top-cited studies on vaccine: a bibliometric analysis

Objective: The objective of this study was to analyze the 100 most cited studies on vaccine.Methods: A comprehensive search of studies on vaccine was performed in the Web of Science Core Collection without year or language restrictions. The 100 top-cited studies were retrieved after screening abstracts or full-texts. The outcomes of bibliometric analysis included citation time, citation density, journal name, impact factor, publication year, article type, category, open access, and country of origin.Results: The citation times for the 100 top-cited studies ranged from 593 to 2406, with a median citation times of 834. The 100 top-cited studies were published in 32 journals, and the journal with the most studies was New England Journal of Medicine (n = 20). They were published between 1969 and 2012, and 4 authors published at least 2 studies as the first author. The USA contributed the most studies (n = 70), followed by Switzerland (n = 4), England (n = 4) and Finland (n = 4). Eighty-one studies were published as Article, while 19 were Review. Eleven studies were about vaccine for therapeutic and 68 studies were about vaccine for prophylactic.Conclusions: This is the first bibliometric analysis to provide a detailed list of the 100 most-cited studies on vaccine and helps to recognize the quality of the works, discoveries, and trends in the field.

Probiotics for preventing acute otitis media in children

BACKGROUND

Acute otitis media (AOM), or acute middle ear infection, is one of the most frequently occurring childhood diseases, and the most common reason given for prescribing antibiotics in this age group. Guidelines often recommend antibiotics as first-line treatment for severe AOM. However, antibiotics also lead to antibiotic resistance, so preventing episodes of AOM is an urgent priority.

OBJECTIVES

To assess the effects of probiotics to prevent the occurrence and reduce the severity of acute otitis media in children.

SEARCH METHODS

We searched CENTRAL, PubMed, Embase, and three other databases (October 2018), two trial registers (October 2018), and conducted a backwards and forwards citation analysis (August 2018). We did not apply any language, publication date, or publication status restrictions.

SELECTION CRITERIA

Randomised controlled trials (RCTs) of children (aged up to 18 years), comparing probiotics with placebo, usual care, or no probiotic.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed the eligibility of trials for inclusion and risk of bias of the included trials, and extracted data using pre-piloted data extraction forms. We analysed dichotomous data as either risk ratio (RR) or odds ratios (OR) and continuous data as mean differences (MD).

MAIN RESULTS

We included 17 RCTs involving 3488 children, of which 16 RCTs were included in the meta-analyses. Of the 16 RCTs that reported the mean age of children, mean age overall was 2.4 years; in 4 RCTs the mean age of children participating in the trial was less than 1 year old; in 2 RCTs the mean age was between 1 and 2 years old; and in 10 RCTs the mean age was older than 2 years. Probiotic strains evaluated by the trials varied, with 11 of the included RCTs evaluating Lactobacillus-containing probiotics, and six RCTs evaluating Streptococcus-containing probiotics.The proportion of children (i.e. the number of children in each group) experiencing one or more episodes of AOM during the treatment was lower for those taking probiotics (RR 0.77, 95% confidence interval (CI) 0.63 to 0.93; 16 trials; 2961 participants; number needed to treat for an additional beneficial outcome (NNTB) = 10; moderate-certainty evidence).Post hoc subgroup analysis found that among children not prone to otitis media, a lower proportion of children receiving probiotics experienced AOM (RR 0.64, 95% CI 0.49 to 0.84; 11 trials; 2227 participants; NNTB = 9; moderate-certainty evidence). However, among children who were otitis prone, there was no difference between probiotic and comparator groups (RR 0.97, 95% CI 0.85 to 1.11; 5 trials; 734 participants; high-certainty evidence). The test for subgroup differences was significant (P = 0.007).None of the included trials reported on the severity of AOM.The proportion of children experiencing adverse events did not differ between the probiotic and comparator groups (OR 1.54, 95% CI 0.60 to 3.94; 4 trials; 395 participants; low-certainty evidence).Probiotics decreased the proportion of children taking antibiotics for any infection (RR 0.66, 95% CI 0.51 to 0.86; 8 trials; 1768 participants; NNTB = 8; moderate-certainty evidence). Test for subgroup differences (use of antibiotic specifically for AOM, use of antibiotic for infections other than AOM) was not significant.There was no difference in the mean number of school days lost (MD -0.95, 95% CI -2.47 to 0.57; 5 trials; 1280 participants; moderate-certainty evidence). There was no difference between groups in the level of compliance in taking the intervention (RR 1.02, 95% CI 0.99 to 1.05; 5 trials; 990 participants).Probiotics decreased the proportion of children having other infections (RR 0.75, 95% CI 0.65 to 0.87; 11 trials; 3610 participants; NNTB = 12; moderate-certainty evidence). Test for subgroup differences (acute respiratory infections, gastrointestinal infections) was not significant.Probiotic strains trialled and their dose, frequency, and duration of administration varied considerably across studies, which likely contributed to the substantial levels of heterogeneity. Sensitivity testing of funnel plots did not reveal publication bias.

AUTHORS' CONCLUSIONS

Probiotics may prevent AOM in children not prone to AOM, but the inconsistency of the subgroup analyses suggests caution in interpreting these results. Probiotics decreased the proportion of children taking antibiotics for any infection. The proportion of children experiencing adverse events did not differ between the probiotic and comparator groups. The optimal strain, duration, frequency, and timing of probiotic administration still needs to be established.

[Mortality attributable to influenza in pre-vaccination and post-vaccination periods in Argentina: an ecological study (2002-2016)Mortalidade atribuível à gripe no período pré-vacinal e pós-vacinal na Argentina: estudo ecológico (2002-2016)]

OBJECTIVES

Compare mortality from severe acute respiratory infection (SARI) attributable to influenza between pre-vaccination (pre-V) and post-vaccination (post-V) periods, to determine the historical evolution and seasonality of time series between 2002 and 2016, and to estimate the risk of death in children between 6 and 23 months of age, using a statistical model.

METHODS

Time-series study using official mortality data from the official statistical database on deaths. ICD-10 codes between J09-18.9 and J22X were considered to represent SARI. Crude rates and age-adjusted rates (AAR) were calculated, and pre-V (2002-2009) and post-V (2010-2016) periods were compared using the chi-squared (χ2) test. The best statistical model was the one that compared deaths from SARI in children during 2002 with other years. The data were analyzed with R programming (p <0.05).

RESULTS

4.6% of deaths (301,747) were from SARI, with a median age of 82 years. The percentage of deaths under age 2 declined in the post-V period (from 2.34% to 0.99%, p < 0.05). Marked seasonality was observed in winter. The AAR in persons over age 64 rose from 259.8 per 100,000 population (pre-V) to 328.6 (post-V) (p < 0.05). In children, the crude rate dropped significantly. Compared with the year 2002, there was a significantly lower estimated risk of dying from SARI during the three years post-V.

CONCLUSIONS

The reduction in mortality from influenza in Argentina was more pronounced in children, with an estimated 3.5 fewer child deaths from SARI per month.

Burden, effectiveness and safety of influenza vaccines in elderly, paediatric and pregnant populations

Vaccination is the most practical means available for preventing influenza. Influenza vaccines require frequent updates to keep pace with antigenic drift of the virus, and the effectiveness, and sometimes the safety, of the vaccine can therefore vary from season to season. Three key populations that the World Health Organization recommends should be prioritized for influenza vaccination are pregnant women, children younger than 5 years of age and the elderly. This review discusses the burden of influenza and the safety and effectiveness profile of influenza vaccines recommended for these groups.

Estimating Vaccine-Driven Selection in Seasonal Influenza

Vaccination could be an evolutionary pressure on seasonal influenza if vaccines reduce the transmission rates of some ("targeted") strains more than others. In theory, more vaccinated populations should have a lower prevalence of targeted strains compared to less vaccinated populations. We tested for vaccine-induced selection in influenza by comparing strain frequencies between more and less vaccinated human populations. We defined strains in three ways: first as influenza types and subtypes, next as lineages of type B, and finally as clades of influenza A/H3N2. We detected spatial differences partially consistent with vaccine use in the frequencies of subtypes and types and between the lineages of influenza B, suggesting that vaccines do not select strongly among all these phylogenetic groups at regional scales. We did detect a significantly greater frequency of an H3N2 clade with known vaccine escape mutations in more vaccinated countries during the 2014⁻2015 season, which is consistent with vaccine-driven selection within the H3N2 subtype. Overall, we find more support for vaccine-driven selection when large differences in vaccine effectiveness suggest a strong effect size. Variation in surveillance practices across countries could obscure signals of selection, especially when strain-specific differences in vaccine effectiveness are small. Further examination of the influenza vaccine's evolutionary effects would benefit from improvements in epidemiological surveillance and reporting.

The Future of Influenza Vaccines: A Historical and Clinical Perspective

For centuries, the development of vaccines to prevent infectious disease was an empirical process. From smallpox variolation in Song dynasty China, through the polysaccharide capsule vaccines developed in the 1970s, vaccines were made either from the pathogen itself, treated in some way to render it attenuated or non-infectious, or from a closely related non-pathogenic strain. In recent decades, new scientific knowledge and technologies have enabled rational vaccine design in a way that was unimaginable before. However, vaccines optimal against some infectious diseases, influenza among them, have remained elusive. This review will highlight the challenges that influenza viruses pose for rational vaccine design. In particular, it will consider the clinically beneficial endpoints, beyond complete sterilizing immunity, that have been achieved with vaccines against other infectious diseases, as well as the barriers to achieving similar success against influenza.

Neonatal Immunity, Respiratory Virus Infections, and the Development of Asthma

Infants are exposed to a wide range of potential pathogens in the first months of life. Although maternal antibodies acquired transplacentally protect full-term neonates from many systemic pathogens, infections at mucosal surfaces still occur with great frequency, causing significant morbidity and mortality. At least part of this elevated risk is attributable to the neonatal immune system that tends to favor T regulatory and Th2 type responses when microbes are first encountered. Early-life infection with respiratory viruses is of particular interest because such exposures can disrupt normal lung development and increase the risk of chronic respiratory conditions, such as asthma. The immunologic mechanisms that underlie neonatal host-virus interactions that contribute to the subsequent development of asthma have not yet been fully defined. The goals of this review are (1) to outline the differences between the neonatal and adult immune systems and (2) to present murine and human data that support the hypothesis that early-life interactions between the immune system and respiratory viruses can create a lung environment conducive to the development of asthma.

Immune History and Influenza Vaccine Effectiveness

The imperfect effectiveness of seasonal influenza vaccines is often blamed on antigenic mismatch, but even when the match appears good, effectiveness can be surprisingly low. Seasonal influenza vaccines also stand out for their variable effectiveness by age group from year to year and by recent vaccination status. These patterns suggest a role for immune history in influenza vaccine effectiveness, but inference is complicated by uncertainty about the contributions of bias to the estimates themselves. In this review, we describe unexpected patterns in the effectiveness of seasonal influenza vaccination and explain how these patterns might arise as consequences of study design, the dynamics of immune memory, or both. Resolving this uncertainty could lead to improvements in vaccination strategy, including the use of universal vaccines in experienced populations, and the evaluation of vaccine efficacy against influenza and other antigenically variable pathogens.